Study on the chemical evolution of planetary materials and the origin of meteorites inferred from variable analyses of cosmogenic nuclides

利用12块火星陨石、12块辉石(顽辉石)、8块吉林球粒陨石和15块来自阿波罗16号和17号着陆点的月球球粒陨石，研究了宇宙射线与行星物质的相互作用。研究结果表明：(1)在12块火星陨石中，有6块陨石具有中子俘获的Sm和Gd同位素特征、稀有气体的同位素变化特征以及宇宙成因同位素的丰度。考虑到由稀有气体分析估算的宇宙射线暴露年龄与由Sm和Gd同位素测量得到的辐照中子注量之间的相关性很小，一些火星陨石经历了多阶段的辐照。这揭示了火星上陨石预辐射的可能性。(2)即使在同一块陨石中，Pesyanoe和Khor Tomeki等陨石的中子注量计算结果也有很大的差异，说明了奥白云母体风化层中的辐射历史。中子注量和宇宙线暴露年龄之间的系统数据表明，奥布里特分为只受空间照射的亚群和有风化历史的亚群。(3)从Apollo-16和Apollo-17钻杆的中子地层学可以讨论月球表层过程。中子注量率的深度分布表明，在风暴石沉积之后发生了大的混合事件，并且风暴石主要由两块石板组成。

Twelve martian meteorites, twelve aubrites (enstatite achondrites), eight fragments from the Jilin chondrite and fifteen lunar regoliths from Apollo 16 and 17 landing sites, were used in this research to study the interaction of cosmic rays with planetary materials. The samples were characterized from neutron-captured isotopic shifts of Sm and Gd, noble gasses isotopic variations, and abundances of cosmogenic isotopes such as ^<10>Be and ^<41>Ca.New findings from this research are as follows : (1) Neutron captured Sm and Gd isotopes were found in six of twelve martian meteorites. Considering little correlation between cosmic-ray exposure ages estimated from noble gas analysis and irradiated neutron fluence from Sm and Gd isotopic measurements, some of martian meteorite experienced multi-stage irradiation. This reveals a possibility of pre-irradiation of the meteorites on Mars. (2) The calculated neutron fluences for some aubrites such as Pesyanoe and Khor Temiki show significant variations even in the same meteorite, which suggests the irradiation history in the regolith of the aubritic parent body. The systematic data between neutron fluences and cosmic-ray exposure ages suggest the subdivision of aubrites into subgroups with only space irradiation and a subgroup with regolith history. (3) Lunar regolith processes can be discussed from neutron stratigraphy of the Apollo-16 and 17 drill stems. The depth profiles of neutron fluences suggest that large mixing events occurred after deposition of the regoliths and that the regoliths consists mainly of two slabs.